The invention relates to a tyre building drum having a turn-up mechanism for use in building an unvulcanised tyre using rubber tyre components that may or may not have been provided with reinforcement cords and two bead cores that may or may not have been provided with an apex.
A known tyre building drum is provided with a basic part having a central shaft, two ring segments (also called clamping mechanisms) placed around the shaft and spaced apart from each other, for supporting the bead cores and means for radially expanding the part of the tyre components that is situated within the ring segments. On either side outside of the ring segments, the tyre building drum is provided with a set of axially extending arms (also called turn-up or folding arms), wherein at a first free outer end oriented towards the ring segment each arm is provided with a first turn-up member, generally a turn-up roller, and at an opposite second outer end they are hinged to an axially shiftable arm support. Near the first outer end at least a part of each arm may be provided with means for supporting the tyre component, alternatively the tyre building drum may comprise individual support means, that are not connected to the arms.
In a so-called starting position the support means form a circumferential support surface for the tyre components. For the turn-up process use is made of means for shifting the arm supports. On the one hand said means are able to move the second outer ends of both sets of arms axially towards each other in a first direction. Because simultaneously the part of the tyre components that is situated within the ring segments is expanded, the arms will be subjected to a tilting in radial planes towards a tilting position, as a result of which the first outer ends move axially and radially while pressing the part of the tyre components that was originally outside of the ring segments against the expanded part of the tyre components that is situated within the ring segments. On the other hand said means ensure that the arms can be moved back from the tilting position to the starting position, because the means axially move the arm supports apart in a second direction, opposite the first direction.
Such tyre building drums provided with a turn-up mechanism, are generally known. They may be designed as tyre building drum on which the tyre components, in particular liner and carcass layers and sides are supplied and of which a cylindrical casing is being made, and also bead cores are supplied, after which the cylindrical casing on the tyre building drum is expanded into a shaped torus shape, in which the sides of the casing are turned up about the bead cores by means of the turn-up mechanism. They may also be designed as a shaping drum, to which an already formed cylindrical carcass casing has been supplied.
Such a tyre building drum with turn-up mechanism is among others known from EP-A-1.562.738. During the turn-up process, in which the, arms tilt, the parts of the tyre components situated on the support means shift over the support means towards the turn-up member (turn-up roller) to be discharged from there. Due to a mechanic coupling the sets of hinging arms on either side can be moved synchronously from the starting position to the tilting position outside of the ring segments. Although the known tyre building drum usually functions satisfactorily and produces accurate tyres within the set tolerances, it has turned out that in practice a number of produced tyres were of inferior quality.